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1. Introduction
The first known tornado forecast in Europe occurred on 25 June 1967 when meteorologists from the Royal Netherlands Meteorological Institute (KNMI) recognized that, following several tornadoes upstream over northern France on 24 June, the synoptic pattern was not changing overnight. Dutch weatherman Joop den Tonkelaar appeared on an early morning radio show on 25 June and warned about the possibility of tornadoes over the Netherlands later that day. His forecast was based on a stationary synoptic-scale pattern and a similar situation in the Netherlands as in France the previous day. This insight formed the first tornado forecast based purely upon a forecast in Europe (Rauhala and Schultz 2009), although KNMI later changed the forecast from “possible tornadoes” to “possible severe wind gusts” to avoid public panic (BN DeStem 2017). den Tonkelaar's forecast verified with two F3 tornadoes over the Netherlands, as well as two others over France and Belgium. This kind of pattern recognition by Joop den Tonkelaar was similar to that employed by Miller and Fawbush in the first tornado forecast in the United States in 1948 (Grice et al. 1999). Although the first tornado forecasts by Miller and Fawbush drove many advances in the science of tornado prediction in the United States (Grice et al. 1999), the forecast by KNMI did not spark the same type of changes within European meteorological services, with only KNMI issuing forecasts for waterspouts as of 2015 (Holzer et al. 2015).
The KNMI forecast of 25 June 1967 was for what became the second day of the most damaging tornado outbreak in modern western European history in terms of fatalities and property damage-and second for all of Europe behind the 9 June 1984 outbreak in Russia (Finch and Bikos 2012; Antonescu et al. 2017). Combined, the outbreak of 24-25 June 1967 caused 232 injuries, 15 fatalities (Bordes 1968), and an estimated EUR 70-100 million in damages ($68-96 million 2019 U.S. dollars) (Antonescu et al. 2017). The outbreak consisted of one F2 tornado, four F3 tornadoes, one F4 tornado, and one F5 tornado1-one of only three documented F5s in Europe since 1900 (Groenemeijer et al. 2017). The sensitivity of the number of fatalities and buildings damaged to the specific location of the tornadoes in...